Move some config description from Configuration.md to the Broker and Historical config pages
Merge pull request #947 from metamx/configUpdates

Move some config description from Configuration.md to the Broker and Historical config pages
Modify StupidPool usage

* Change StupidPool to be a "ResourcePool", which is essentially a supplier of ResourceHolders
* Change StupidPool to use a concurrent queue
* Add MappedBufferPool which pulls resources from an expanding memory mapped file